The US is facing killer temperatures lower than -56C in the worst weather for 20 years.

A blast of polar air following snow in northern states is expected to push temperatures down to -35C (-31F).

And with the windchill factor, the vortex of counterclockwise cold dense air could plunge them further to -56.7C.

Treacherous travel conditions already disrupting north-eastern states are spreading to the north-west. In Aspen, Colorado, one person was killed and two were injured when a plane burst into flames after trying to land in snowy conditions.